Highly efficient transonic laminar flow wing

ABSTRACT

Improved supersonic laminar flow wing structure, on a supersonic aircraft, having strake extending forwardly of the wing inboard extent, and reversed fillet at strake junction with the wing leading edge.

This application is a continuation-in-part of U.S. Ser. No. 11/974,802,filed Oct. 16, 2007 now U.S. Pat. No. 7,946,535.

BACKGROUND OF THE INVENTION

This invention relates generally to laminar flow high speed aircraftwing configurations adapted for efficient operations at high subsonicspeeds and lower supersonic speeds and (or generally, transonic speeds).We have found that the low sweep thin laminar flow wing type originallyintended for efficient supersonic cruise also has, with minorvariations, excellent performance at transonic speeds. Accordingly, justas for the efficient supersonic laminar flow wing, several improvementsare useful both at design cruise condition, as well as at the lowerspeeds required during takeoff and landing. More specifically itconcerns improvements in the following configuration areas:

a) strake,

b) raked wing tip,

c) reversed fillet wing-strake junction,

d) inboard leading edge flap,

e) hybrid plain-split flap system.

Prior Richard Tracy U.S. patents disclose a laminar flow wing forefficient supersonic flight (U.S. Pat. No. 5,322,242, U.S. Pat. No.5,518,204, U.S. Pat. No. 5,897,076 and U.S. Pat. No. 6,149,101). Asubsequent Richard Tracy et al U.S. Pat. No. 7,000,870 discloses similarwing designs for efficient flight at transonic speeds. These aresomewhat thicket than the supersonic laminar flow wing in terms of theratio of maximum thickness to chord, but are of similar type, havinggenerally biconvex airfoils, relatively low sweep, and a sharp orslightly blunted leading edge. They also have similar characteristics atthe low speeds and higher angles of attack associated with landing andtakeoff. Thus aircraft with this type of transonic laminar flow wingbenefit from improvements similar to those disclosed for the supersoniclaminar flow wing in the patent application Ser. No. 11/975,802 of whichthis is a continuation in part.

The areas of improvement, which principally benefit the low speedcharacteristics of aircraft using the wing, are enumerated above (athrough e). The wing described in the prior Tracy patents has a sharp,modified biconvex airfoil, with less than about 30° leading edge sweepin order to maintain an attached shock at supersonic cruise conditions,and thickness-chord ratio (t/c) of about 2% (or 3% for the transonicwing) as a span-wise average over the majority of the outer portion ofthe wing. The latter excludes a zone near the inboard end, which may bethicker, up to about 4% t/c (or more for the transonic wing) incombination with fuselage area ruling.

There are several unique characteristics of the supersonic and transoniclaminar flow wing which pose challenges, especially in low speed flight.These include (1) its sharp or slightly blunted leading edge whichcauses a separation “bubble” at almost any angle of attack in subsonicflight, (2) its extremely thin airfoil which imposes a structural weightpenalty as aspect ratio is increased, and (3) the un-swept leading edgewhich limits the effectiveness of “area ruling” of the body to minimizetransonic wave drag. These (and other characteristics) are unique to thesupersonic laminar wing and are substantially mitigated by the hereinclaimed improvements, acting individually or together, in combinationwith this type of wing.

SUMMARY OF THE INVENTION

Two of such improvements utilize features which have not been used inaircraft design, in conjunction with the type of laminar flow wing underconsideration. These are a “strake” and a “raked” tip, as describedbelow. Three additional features are unique to the supersonic ortransonic laminar flow wing. These are a “reverse fillet”, a deployabledevice at the inboard end of the leading edge, and a “hybrid” flapsystem. All five are described below.

Strake

The strake is a highly swept portion of the wing between the fuselageand the inboard end of the low sweep main wing panel. The strake'sleading edge is preferably swept forward of the wing to an intersectionwith the fuselage, and its trailing edge may be a continuation of theouter wing trailing edge, or may be swept further aft to a fuselageintersection. The strake leading edge is preferably highly swept, and inthe case of a supersonic design, more than the Mach angle at the maximumsupersonic cruise speed in order to have a “subsonic leading edge” (theMach number component normal to the leading edge being subsonic). Thiscondition assures a detached shock wave and permits the leading edge ofthe strake to be somewhat blunt and cambered for less supersonic drag,giving an increased maximum “lift coefficient” for enhanced low speedlift capability.

The strake performs several functions in addition to increasing maximumlift in the present application, while favorably affecting transoniccruise performance. These are as follows: 1. Increases the span of thewing for a given outer wing panel length, for improved lift efficiencywith less structural weight penalty, 2. Improves the longitudinaldistribution of fuselage and wing cross sectional area (area ruling) forlower transonic wave drag, 3. Provides additional volume for fuel in theforward part of the aircraft, 4. Creates a leading edge vortex on thestrake at moderate and high angles of attack in subsonic flight whichtends to keep the flow attached over the upper inboard strake surfacefor better lift and engine inlet flow quality for inlets lapping thewing on either side of the fuselage, 5. Limits cross-flows over theinboard portion of the wing, and 6. Provides a structural hard point forlanding gear mounting and space for gear retraction.

Raked Tip

The “raked tip” is a highly swept lateral edge, or wing tip, of thewing, which may have either a sharp or slightly blunted edge as long asit is highly swept, and in the case of a supersonic design, more thanthe Mach angle at the maximum supersonic cruise speed in order to have a“subsonic leading edge”. The tip adds two important attributes to thetype of wing under consideration.

It adds to the span and thus increases aspect ratio without as muchassociated drag-causing wetted area and structural bending as aconventional rounded or blunt tip. More importantly, in low speed flightat up to moderate angles of attack, it generates a “rolled up” vortex,which helps keep the airflow attached to the upper surface of the outerwing. The attached tip vortex delays the growth of the leading edgeseparation bubble and resultant loss of lift over the outer portion ofthe wing. This, in turn, increases the maximum lift of the wing andprevents, or delays, the inboard movement of the tip vortex associatedwith loss of outer wing lift. The result is a lower change with angle ofattack of the wing downwash angle at the horizontal tail, providinggreater longitudinal stability and mitigating the tendency to pitch up.

Reversed Fillet

The wing junction with the strake (or the fuselage) on most aircraft issubject to detail treatment in form of a “fillet” or concave surfaceblending smoothly with the wing and fuselage surfaces. This fillet isgenerally associated with a concave curve in plan view between theleading edge and the fuselage.

Avoiding excessive boundary layer cross-flow at the junction of the wingleading edge to strake (or fuselage) can be very difficult because ofthe large “up-wash” flow at the junction, resulting in locally highpressure gradients on the wing surface. These gradients can causelocally critical levels of boundary layer cross-flows, which can in turndestabilize the laminar boundary layer, resulting in a turbulentboundary layer and higher skin friction drag over a substantial portionof the inner wing. However by making the leading edge profile convex atthe strake (or fuselage) junction, so as to eliminate, or even slightlyreverse, the leading edge sweep locally at that junction, cross-flowscan be reduced to below critical levels and transition to turbulencesubstantially reduced.

Inboard Leading Edge Flap

A second consequence of the strong up-wash near the leading edgejunction with the strake (or fuselage), in combination with the sharpleading edge is a premature growth of the leading edge separation“bubble” leading to early loss of lift over the inboard portion of thewing. Full span leading edge flaps can delay the formation and growth ofthe leading edge “bubble”, but such devices are mechanically awkwardwith the very thin, sharp or slightly blunted leading edge of thelaminar wing. In addition they are difficult, if not impossible, toimplement without any surface gap or disturbance which would precludelaminar flow.

A more practical solution is a leading edge flap extending over only theinboard 15%, or so, of the wing panel span outboard of the strake orfuselage, where the up-wash is greatest. Such a device, for example aKruger flap extending forward of the leading edge, has been shown byproprietary tests to be very effective on this type of wing. It can bedeployed from the strake (or fuselage) with little or no leading edgemechanical attachment, by various means such as translating the flaplaterally from a cavity in the strake (or fuselage), or by swinging itabout a vertical pivot axis from a stowed position in the strake (orfuselage).

Hybrid Plain-Split Flap

The thin laminar flow wing is not well-suited to multi-element slottedflaps, slotted fowler flaps, or even “zap” flaps, because of lack ofinterior space and the drag penalty of external hinges and tracks. Forthese reasons a plain hinged trailing edge flap is the most practicalapproach. However the lift increment which can be generated, especiallywith the sharp leading edge wing, is limited by separation of the flapupper surface.

A simple split flap, in which only the lower surface is deflected, hasslightly higher maximum lift capability than a plain flap, but at apenalty in drag. In any case, a split flap would not be consistent withthe need for small amounts of flap deflection for efficient transoniccruise, which is required for most applications of the laminar transonicwing.

For this type of wing a hybrid flap system comprised of split and plainflap combination offers unique advantages. The hybrid split flap isconfigured such that a portion of the flap lower surface can deflectdown relative to the plain flap. The split flap hinge line can beco-located with the plain flap hinge, or preferably aft of it, near midchord of the plain flap. When deflected, the split flap delaysseparation on the upper surface of the plain flap by lowering the wakepressure and reducing the adverse pressure gradient at the plain flapupper surface trailing edge. Since the outer portions of the plain flapare the most vulnerable to such separation, the split flap alsomitigates tip stall and the increased downwash that would result asdescribed in connection with the raked tip above. Small flap deflectionsfor transonic cruise can be accomplished with the plain flap, keepingthe split flap closed. Because of the very thing bi-convex airfoilsemployed on the transonic laminar flow wing, and unlike conventionalairfoils, the flap external contours are virtually flat over themajority of their chord length.

DRAWING DESCRIPTION

FIG. 1 herein shows a transonic aircraft wing, strake, flaps and leadingedge flap;

FIG. 2 is a view of a supersonic wing airfoil of a laminar flow wing,showing trailing edge and inboard leading edge flap structures;

FIG. 3 is a view of a wing, showing locations of the FIG. 3 flapstructure;

FIG. 4 is a view like FIG. 3, but showing actuators;

FIGS. 4 a, 4 b and 4 c are views like FIG. 4, but showing differentdeflected positions of plain and split flaps;

FIG. 5 is a view of a representative rotary hinge flap actuatorassembly;

FIG. 5 a is like FIG. 5 except flaps are downwardly deployed;

FIG. 6 is a view of a modified aircraft; and

FIG. 7 is a plan view of a modified aircraft.

DETAILED DESCRIPTION

In the drawings, the preferred transonic aircraft 10 has a fuselage 11,thin, laminar flow wing 12 including left and right wing sections 12 aand 12 b, jet engines 13 closely proximate opposite sides of thefuselage, and tail 14.

The strake is shown at 15, as a highly swept portion of the wing betweenthe fuselage 11 and the inboard end 16 of the low sweep main wing panel.Other strake characteristics are referred to above.

The raked tip of each wing section is shown at 17, and hascharacteristics as referred to above.

Reversed fillet configuration, for each strake-fuselage junction leadingedge, is indicated at 19, and has characteristics as referred to above.See also FIGS. 6 and 7.

The inboard leading edge flap is shown, for each wing section, at 18,and has characteristics as referred to above, and may have associationwith cavities in the fuselage or strake.

Hybrid plain-split flap, for each wing section, is provided at 21, andhas characteristics as referred to above, and includes plain flap 21 aand split flap 21 b. In the preferred embodiment rotary hinge actuatorscontained within the airfoil contour are employed, although conventionallinear actuators combined with bell crank linkages could also beemployed. Actuators for the plain flap 21 a and split flap 21 b areindicated at 35 a and 35 b respectively, and may have associationcavities in the wing, fuselage or strake. The hinge line for 21 b is at21 c. In FIG. 3, the hinge line for the split flap may be co-located ator aft of 21 c, with respect to plain flap 21 a.

In FIG. 4, the typical transonic cruise configuration is depicted withplain flap 21 a and split flap 21 b elements in their faired positions.

In FIG. 4A, a typical subsonic cruise position is depicted with plainflap 21 a deflected through a small angle with split flap 21 bundeflected and faired with respect to flap 21 a. In FIG. 4B, a takeoffposition is depicted with additional downward deflection of the plainflap 21 a and a small deflection of the split flap element 21 b relativeto 21 a. Leading edge flap 18 is showed deployed for this condition.

In FIG. 4C, a landing configuration is depicted with additional downwarddeflection of both plain flap element 21 a and split flap element 21 b.

FIGS. 5 and 5 a show details of actuators 50 usable in FIGS. 4, 4A, 4Band 4C, and confined between planes defined by outer (uppermost andlowermost) surfaces of the plain and split flaps.

FIG. 5 illustrates a configuration of rotary geared actuators (RGA) toattach to and deflect the hybrid flap system. The forward attaching earsof actuators 35 a are connected to the structure of wing 12 and plainflap 21 a is attached to the aft ears of 35 a. The aft ears rotaterelative to the forward ears via internal gearing of the 35 a RGA, driveshafts, motor, and gearbox 36 a effecting the deflection of flap 21 aand split flap 21 b which is attached to it. Similarly, the forwardattaching ears of actuators 35 b are connected to the structure of plainflap 21 a and split flap 21 b is attached to the aft ears of 35 a. Theaft ears rotate relative to the forward ears via drive shafts, motor,and gearbox 36 b effecting the deflection of split flap 21 b relative to21 a. This system allows for independent deflections of the split flapand plain flap segments. A system where split flap deflection isdependent on plain flap deflection may be effected by a single motor andinterconnecting drive shafts and gear boxes. A system driven via linearactuators (such as hydraulic cylinder or jack screw) and bell cranklinkages may be employed.

FIG. 5 a illustrates the plain flap deflected relative to the wing, andthe split flap deflected relative to the plain flap segment.

FIG. 5 also shows actuator position conformance to the flatnessconfiguration of the plain and split flaps.

In the aircraft of FIG. 6, the inboard leading edge flap 18 a is shownin the stowed (retracted) cruise position. Numeral 18 b shows the righthand leading edge flap in extended position at the right hand (12 b)wing section. Positions at 18 a and 18 b have characteristics asreferred to above, and may have association with cavities in thefuselage or strake, as indicated. When the leading edge flap isextended, it projects in superposed relation to the angularly reversedfillet, for operation at lower speeds.

FIG. 7 illustrates the top view of an aircraft 40 without the strakeelement but incorporating the reverse fillet leading edge intersection19 intersecting the side of the fuselage 11. The reverse fillet, leadingedge extends angularly toward the fuselage, also longitudinallyrearwardly.

What is claimed is:
 1. Improved high speed laminar flow wing structure,on an aircraft, having in combination the following: a) strake extendingforwardly of the wing inboard extent, b) reversed fillet at strakejunction with the wing leading edge, c) plain flap and hybridplain-split flap structures and flap deflecting actuators thereforcarried at the wing trailing edge, rearward of the strake and reversedfillet, said actuators having a pivoting axis that is collinear with apivoting axis of said split flap.
 2. The combination of claim 1 whereinsaid wing structure includes the following: i) plain flap hinge line,ii) a hybrid plain-split flap hinge locus spaced aft of the plain flaphinge line, iii) said actuators at said hinge line and at said hingelocus to controllably and independently deflect said plain flap and saidhybrid plain-split flap, downwardly, said actuators respectivelyprojecting above said hinge line and above said hinge locus.
 3. Thecombination of claim 1 wherein the plain flap is positioned to bedownwardly deflected at a first angle and the split flap is positionedto be downwardly deflected to become angled at or below the plain flap.